The present invention relates generally to active array systems, and more particularly, to active array systems that process simultaneous multiple beams/frequencies and can operate over a very wide frequency range and thus overcome the limitations of conventional systems.
Conventional phased array systems have limited operating frequency range, have a large weight and size, and are generally restricted to single beam and narrow frequency operation range. In order to steer multiple beams at different frequencies, conventional phased array systems would need to use multiple manifolds, one for each independent beam and or frequency.
The present invention replaces and improves upon a technique for generating a plurality of signals for RF transmission having variable phase differences described in U.S. Pat. No. 3,090,928, assigned to the assignee of the present invention, and also described in a recent MTT paper entitled "Frequency Controlled Antenna Beam Steering", published in the 1994 IEEE MTT-S Digest, CH33694/94/0000 1549501,00.
The basic concept disclosed in that patent and paper is to use a prior frequency-scanned radar beam steering transmission technique that used a series delay line "traveling wave" feed to provide progressive phase delays needed to steer (scan) beams of an antenna array. Thus, the typical phase shifters needed to steer a phased array are eliminated. That prior technique, implemented before the above-referenced patent, had the disadvantage of having the radiated frequency directly dependent on the selected beam pointing direction.
The technique described in that patent uses a dual RF delay series traveling wave feed where the radiated frequency .omega..sub.1 is generated by mixing a frequency (.omega.-.omega..sub.1) with a tuning (steering) frequency (.omega.). The tuning frequency .omega. is sent down one of the delay lines and tapped off to each radiator from equally spaced ("time") delay taps. Another frequency that is the combination of .omega. and .omega..sub.1, i.e., (.omega.-.omega..sub.1), is sent down the other (dual) delay line from the opposite or other side of a line feed. RF mixing of the signals on each delay line is used to generate the radiated frequency.
The fact that the tuning frequency (.omega.) is present in both delay lines, that is, separately in one delay line and as a combination with the radiated frequency .omega..sub.1 in the other delay line, provides the desired result after mixing of an operating radiated frequency (.omega..sub.1) that does not change as the tuning frequency (.omega.) is changed (tuned) to steer the array beam. The tuning frequency is canceled out by virtue of mixing the two frequencies at each radiator of the phased array and filtering is used to obtain only the .omega..sub.1 difference frequency as the radiated signal.
The correct progressive phase is generated with a modulo 2.pi. residue, wherein the modulo 2.pi. residue adds or subtracts multiples of 2.pi. or 360.degree. values to a relative phase between radiators, and thus has no effect on beam steering. Thus, the operating frequency that is generated and sent to each radiator after mixing and filtering has the correct relative phase to steer the antenna array. This same concept is also described in the referenced paper.
Accordingly, it is an objective of the present invention to provide for active array systems that process both transmitting and reception at simultaneous multiple beams/frequencies over a wide frequency range, and overcome limitations of conventional phased array systems and improve upon the teachings of the above-referenced patent.